By Lyle McDonald

A Primer on Nutrition Part 2

On Monday, in A Primer on Nutrition Part 1, I discussed essential vs. inessential (aka indispensable vs. dispensable) nutrients along with the basics of both protein and carbohydrates. Today I want to finish taking a look at the basics of nutrition by looking at fat/cholesterol and then wrapping up Ďeverything elseí including alcohol, vitamins/minerals and fiber (somewhat separate from vegetables).

Fat and Cholesterol

Although I recently examined Fat and Cholesterol in some detail in A Primer on Dietary Fats Part 1 and A Primer on Dietary Fats Part 2 back in May, I want to take a briefer, more streamlined look at them in todayís article. Readers wanting more details can click the above links.

Even though they are chemically and nutritionally distinct substances, dietary fat and cholesterol are so linked in the minds of most people that Iím going to discuss them together. As well, along with the never-ending debate over carbohydrates in the diet, the issue of dietary fats is one of almost constant debate in both nutritional sciences and among nutritional experts. Iím not going to get into those debates in any real detail here (since itís about the basics) but interested readers can read Carbohydrate and Fat Controversies Part 1 and Carbohydrate and Fat Controversies Part 2 if they want more details.

First let met get cholesterol out of the way since I donít actually have a tremendous amount to say about it. Cholesterol plays a number of roles in the body not the least of which is involvement in the structure of cell membranes in the body. As well, cholesterol provides the Ďbaseí for the steroid hormones, testosterone, estrogen, progesterone and others are synthesized out of cholesterol in the body.

Of course, when most people hear the word Ďcholesterolí, they immediately think heart disease and, certainly, one aspect of cholesterol metabolism in the body is that it can cause atherosclerotic plaques (essentially the cholesterol builds up in arteries, potentially blocking blood flow).

Please note: I am vastly simplifying a much more complicated topic.

And this tends to be the source of much confusion, especially among the lay public, about diet; they confuse dietary cholesterol intake with blood cholesterol (aka blood lipid) levels. Iíd note, and again this is more complicated than I want to cover here, that blood cholesterol levels are only one of several contributors to the issue of heart disease. Others contribute.

But there tends to be an idea that dietary cholesterol intake is a primary determinant of blood cholesterol levels when, simply, this isnít generally the case. Certainly a percentage of people seem to be sensitive to dietary cholesterol intake (in terms of how their blood cholesterol responds) but, in the majority, dietary cholesterol intake per se has very little impact on blood lipid levels.

As well, your body generally makes more cholesterol (in the liver) than you eat in a day; thatís unless dietary cholesterol intake is exceedingly high. Additionally, the live modifies how much cholesterol it produces depending on daily intake. If dietary cholesterol intake goes up, the liver makes less; if dietary cholesterol intake goes down, the liver makes more. The body is smart that way.

Rather, the types and amounts of dietary fat being consumed play a far larger role in blood lipid levels. Frankly, I donít have much more to say about dietary cholesterol, itís simply not that big of a deal unless you are in that small percentage of folks who are sensitive to it. Rather, I want to talk a bit more about dietary fats.

Of course, a primary role of dietary fats in the body is to be used for energy and it was assumed for many years that this was the only real role of fat, to provide energy storage. This was especially true of stored body fat which was thought for decades to provide only a passive storage depot of energy; rather it turns out that fat cells do much more in the body, producing hormones and such that affect myriad processes elsewhere in the body (a topic Iíve discussed at length on the site and in my books)..

Fats are also found in the cell membranes of various tissues (and the type of fat stored there can affect various cellular processes). As well, fats can be used to make eicosanoids, chemical messengers made from specific fatty acids that affect numerous biological processes. Specific dietary fats can also affect gene expression in certain cells, impacting on things like fat storage and oxidation and many others.

From an energetic standpoint, fats are typically assigned a caloric value of 9 kilocalories/gram (~38 kj/g); there are slight differences between specific fatty acids however. As well, there is some evidence that different fats have a slightly different propensity to be stored vs. burned after consumption although the differences between the fatty acids are relatively small. Iíd mention for completeness that dietary cholesterol has no energetic value to the body.

The biggest controversies regarding dietary fat usually revolve around the health effects of its consumption. Itís not unfair to say that, for many years now, dietary fat has been the whipping boy of the nutritional world (though carbohydrates are taking that role in recent years): fat makes you fat, fat causes heart disease and cancer, fat is probably responsible for terrorism in the US and the decline in the family unit. You name it and the problem has probably been blamed on dietary fat by certain groups. At the other extreme are folks who argue that dietary fats have no health negatives, that they can be consumed effectively without limit or concern.

As with so many extremist stances, the truth is a little different and tends to lie somewhere in the middle.

In the past ten years or so, the issue of fat quality (i.e. type of fat) has become just as important as that of fat quantity (i.e. amount of fat). Simply put: all fats are not the same in terms of their effects on health. As well, whether a specific fat is good, bad or neutral in terms of health depends to a great degree on the context in which itís eaten; this is a concept that neither extremist group can seem to wrap their heads around.

Whether the person is active or inactive, fat or lean, the rest of their diet, gaining or losing weight, and a host of others all contribute to the effect a given fat will have on the body. Iím not going to go into further details here, Iíd suggest you read Carbohydrate and Fat Controversies Part 1 and Carbohydrate and Fat Controversies Part 2 for more details.

In any case, dietary fats are generally divided into four distinct categories, Iím going to look at each in brief next.


Trans-fatty acids are a man-made fat made by bubbling hydrogen through vegetable oil to make it semisolid with a longer shelf-life; Iíd note that there are naturally occurring trans-fatty acids found in foods as well. Margarine is probably the example most readers are familiar with although trans-fatty acids (also called partially hydrogenated vegetable oils) are commonly found in most processed foods (there is currently a big push for trans-fat free foods to be produced commercially).

Of the four types of fats, trans-fatty acids have the least amount of debate around them; their intake at even low levels tends to have exceedingly detrimental impacts on things like blood lipid levels and diabetes risk. Due to the high reliance on processed foods in the modern diet, trans-fatty acid intake is thought to be at least one part of the problems being seen in the modern world (note: there are certainly other contributors).

Saturated Fats

Saturated fats are found almost exclusively in animal products (two exceptions are coconut and palm kernel oil) and are solid at room temperature. Traditionally, the impact of saturated fats on blood lipid levels and heart disease risk has been thought to be universally negative but it turns out to be much more complicated than this. While some saturated fats do reliably raise blood cholesterol levels (primarily due to an impact on liver metabolism), others are completely neutral. Anybody interested in this topic may wish to read the journal article Saturated Fats: What Dietary Intake.

As well, as I mentioned above there is far more to heart disease risk than just blood cholesterol levels. And, as also noted above, the overall impact of any fat (including saturated fats) on health risk depends on the context of their intake. In one context (e.g. low fruit/vegetable/anti-oxidant intake, high stress, inactivity, high body fat, excessive total energy intake), a high saturated fat intake may be exceedigly harmful. In a different context (e.g. high fruit/vegetable intake, low stress, high activity, low body fat, appropriate energy intake), they may have no effect. I hope that any of the pro-saturated fat folks reading this article will read this paragraph a couple of times before they leave me comments about how Iím anti-saturated fats.

Iíd finish by noting that saturated fats are not an essential nutrient. They arenít required for life and, even if they were, the body can produce them from other sources.

Monounsaturated Fats

Monounsaturates are present in almost all foods which contain fat and are liquid at room temperature (quite in fact, the majority of fat in most Ďhigh-fatí foods is monounsaturated). Olive oil is arguably the most well-known of the monounsaturated fats and has received a great deal of attention as a relatively healthy fat. Monounsaturates have a neutral, if not beneficial, effect on health and itís thought that the high olive oil consumption among Mediterraneans is partly responsible for their robust health (there are ceertainly other factors involved here).

Like saturated fats, monounsaturated fats are not an essential nutrients, they may confer health benefits but they are not required for survival.

Polyunsaturated Fats

Polyunsaturated fats are found primarily in vegetable oils and are liquid at room temperature. They are generally claimed to have a positive effect on human health although, as always, things are a little more complicated than that. Polyunsaturated fats come in two major ďflavorsĒ, referred to generally as omega-three and omega-6 fatty acids.

The omega-3 fatty acids include a number of different fatty acids including the Ďparentí fatty acid alpha-linoleic acid (ALA) found in things such as flax oil along with the fish oils (EPA and DHA). I would be surprised if anybody reading this hadnít heard of the fish oils or their benefits. In sum, fish oils do just about everything, they decrease inflammation, help with depression (especially while dieting), decrease enzymes involved in fat storage and increase the levels of enzymes involved in fat burning. Iíd finish by noting that the conversion of ALA to EPA is fairly low and the further conversion of EPA to DHA is basically insignificant. For this reason, taking preformed fish oils is generally required to impact body levels of EPA/DHA to any great degree.

Similarly, the omega-6 fatty acids include a host of different fatty acids including linolenic acid (LA), found in many vegeteable oils, along with things such as arichnidonic acid (AA) which are made from metabolism or LA within the body.

Iíd note that both the w-3 and w-6 fatty acids are part of a more general class of fats called essential fatty acids, that is they are essential nutrients; that is, as explained in A Primer on Nutrition Part 1, they are required for life and cannot be made within the body. In the modern diet, itís generally pretty easy to get w-6 fatty acids through the diet, unless folks consume fatty fish, w-3 are much harder to come by (hence the general need for some type of supplementation).

Now, there is some controversy over w-3 and w-6 intake with excessive w-6 intake being thought to cause some health problems (such as inflammation). In the modern diet, the intake of w-6 fatty acids to w-3 is about 20-25:1 or so and itís been thought that a ratio closer to 1:1 or 4:1 would be healthier with the excessive w-6 intake causes problems. Some groups have even blamed current health problems less on saturated fat intake and more on a high w-6 intake due to the use of vegetable oils in the modern diet.

However, as I discussed in more detail in A Primer on Dietary Fats Part 2, current research calls this into question with mortality rate generally decreasing with increasing w-6 intake and some research suggesting no real impact on inflammation of Ďexcessiveí w-6 intake. Iím not going to go into any real detail here, please read that article for more information.

Dietary Fats: Summing Up

I expect the issue of dietary fats to remain an area of controversy for some time to come. New functions of dietary fats are still being found and the impact of dietary fats on overall health (not simply limited to heart disease) will continue to be examined. As I noted above, I feel that the impact of a given type of dietary fat on health is entirely context dependent, an issue that the individuals involved in both sides of the debate seem to have missed. Since Iíve discussed this in detail in other articles linked in this piece along with touching on it briefly above, I wonít discuss it further.

Everything else: Fiber, Alcohol, Vitamins and Minerals

I recently looked in some detail at fiber in Fiber Ė Itís Natureís Broom and only want to touch on it in brief here. While not an essential nutrient (e.g. you wonít die if you donít eat it), fiber does play a number of important roles in human health in nutrition. If nothing else, high-fiber intakes tend to keep people full and, generally, high-fiber diets are associated with greater weight loss or at least less weight gain. There are other effects as well, see the above article for the details.

Fiber can be subdivided into a variety of different categories but, practically speaking, the main ones of importance are soluble and insoluble fiber. Soluble fibers mix in water and take up a lot of space in the stomach, it also holds food in the stomach longer: this tends to increase feelings of fullness. In contrast insoluble fibers donít mix with water but help with bowel regularity and keep the colon healthy.

Both types of fiber appear to be important to human health and both are found in varying degrees in foods such as fruits and vegetables (grains have varying amounts of fiber depending on how processed they are).

Alcohol isnít really a nutrient in that it provides nothing of actual nutritional value except for calories. Even there, alcohol intake doesnít seem to scale with predicted weight gain although nobody is quite sure why this is the case. Some studies suggest that some alcohol calories go Ďmissingí but nobody can figure out where they are. Alcohol also tends to impact on metabolism in a way that can promote fat gain. Certainly alcohol can have a place in any diet (with a large body of research suggesting that moderate alcohol intake has health benefits depending on the specifics) but excessive amounts can cause varying problems.

Finally there are vitamins and minerals which serve innumerable roles in the body and which include a host of essential nutrients (again, canít be made in the body, required for life). Minerals such as calcium are structural (e.g. bone) along with being involved in cellular signalling. Iron is involved, of course, in the formation of red blood cells, important for overall health and performance. Zinc is involved in immune system function and a host of other processes (including appetite regulation). Vitamins act as nutritional co-factors and are necessary for the body to function optimally.

Vitamins and minerals are found to some degree in all foods with amounts and types depending on the specific food. Fruits and vegetables tend to be nutritional powerhouses in this regards but some vitamins and minerals are optimally consumed in foods of animal origin (for example, the iron in red meat is absorbed roughly ten times better than the iron in vegetable source foods and B12 can only be found Ďnaturallyí in animal source foods).

In that context, Iíd note that a class of nutrients called phytochemicals are only found in plant foods and there is currently a great deal of interest in the health benefits of these compounds. They arenít essential by any stretch but may confer health benefits. Various anti-oxidant nutrients are also found in varying amounts in these foods and, while anti-oxidant supplementation has generally shown little to no real health benefits, diets high in food-based anti-oxidants have been found to confer many health benefits.